The present invention relates generally to wire bonders, and more particularly, to improved ultrasonic transducers for use in ultrasonic wire bonders.
An ultrasonic bonder is comprised of an ultrasonic transducer into which a bonding tool is transversely secured that is used to ultrasonically bond wires to integrated circuits and substrates, and the like. The ultrasonic transducer includes piezoelectric discs that are excited by an alternating voltage to axially move the transducer and consequently "excite" the bonding tool to have a transverse motion (a vibrating reed).
All ultrasonic transducers used in currently available wire bonders cream this vibration at the the bonding tool end of the transducer. The end of the transducer opposite the bonding tool extends into a cylindrical mounting surface or mates with a flat-face mounting surface. A node of the sinusoidal motion is located at the mounting surface and an anti-node is formed at the bonding tool end of the transducer. At the node, axial movement is (ideally) zero while radial movement is a maximum. This corresponds to Poisson's ratio--the ratio of lateral strain to longitudinal strain for a material subjected to uniform longitudinal stresses within a proportional limit.
However, in conventional mounting arrangements for the transducer, the radial movement (strain) acts on mating surfaces of the transducer and mounting surface. The degree of restraint the mount exhibits affects the ultrasonic performance of the transducer. The present invention relieves this restraint, allowing unimpeded ultrasonic movement, better efficiency, and wire bond repeatability.
Furthermore, in conventional ultrasonic transducers, wear occurs in a tool hole in which the bonding tool is secured. This is a result of clamping the bonding tool in the tool hole only at the middle where it is free to rock and lose ultrasonic energy. The clamping force in conventional ultrasonic transducers is perpendicular to the direction of applied ultrasonic motion. The present invention substantially eliminates tool hole wear in the transducer.
Therefore it is an objective of the present invention to provide for an improved ultrasonic wire bonder. It is a further objective of the present invention to provide for an improved ultrasonic transducer for use in ultrasonic wire bonders that substantially eliminates bonding tool-hole wear and improve transducer mounting to provide unimpeded ultrasonic movement, better efficiency, and wire bond repeatability. It is a further objective of the present invention to provide for an axial mounting arrangement for the bonding tool of the wire bonder. It is a further objective of the present invention to provide for driver-node mounting for the transducer in the wire bonder.